Branched Ionomers

ABSTRACT

A branched aromatic ionomer is prepared by co-polymerizing a first monomer having an aromatic moiety and an unsaturated alkyl moiety and a second monomer having an ionic moiety and at least one unsaturated moiety. The ionic moiety may have a cationic group having a valence of +1 or greater. Styrene is among the useful first monomers and sodium methacrylate and zinc dimethacrylate are among the useful second monomers. The branched aromatic ionomers may be used to prepare articles including foamed polystyrene and microwave save dishes and utensils.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to polymers. The present invention particularly relates to ionomer polymers.

2. Background of the Art

In the art of preparing polymers, it may be desirable to impart to or increase the branching of polymer chains. Increased branching may impart physical property changes to the polymer including increased strength, higher temperature performance, and improved hardness. In some instances, increased branching may improve properties such as elastomeric performance and abrasion resistance.

Ionomers are known to be useful in many applications. For example, a polyester ionomer dyeability enhancer may be derived from the reaction residue of an aryl carboxylic acid sulfonate salt, an aromatic dicarboxylic acid, an aliphatic dicarboxylic acid, an aliphatic diol or any of their ester-forming derivatives. A photocurable dental cement may be prepared using a photocurable ionomer, which is defined as a polymer having sufficient pendent ionic groups to undergo a setting reaction in the presence of a reactive filler and water, and sufficient pendent polymerizable groups to enable the resulting mixture to be polymerized, e.g., cured upon exposure to radiant energy.

Another ionomer application is in the area of preparing abrasive surfaces. Ionomers useful in this application are copolymers of ethylene with unsaturated acid salts such as the zinc salt of acrylic acid. Typical commercial products of this type include Aclyn®, Himiran™, Coathylene®, Surlyn® and Escor® polymers. Surlyn®, of course, is a well known component in the covers of some premium golf balls.

SUMMARY OF THE INVENTION

In one aspect, the present invention is a branched aromatic ionomer prepared by co-polymerizing a first monomer having an aromatic moiety and an unsaturated alkyl moiety and a second monomer having an ionic moiety and at least two unsaturated moieties. In this aspect, the ionic moiety has at least two ionizable groups, a cationic group that ionizes to form cations and an anionic group that ionizes to form anions and the cationic group is poly-valent and one capable of forming bridges to other molecules in the presence of ions of a suitable type and concentration.

In another aspect, the present invention is a branched aromatic ionomer prepared by co-polymerizing a first monomer having an aromatic moiety and an unsaturated alkyl moiety and a second monomer having an ionic moiety and at least one unsaturated moiety. In this aspect, the ionic moiety has at least two ionizable groups, a cationic group that ionizes to form cations and an anionic group that ionizes to form anions and the cationic group is a mono-valent group.

Another aspect of the present invention is a process for preparing a branched aromatic ionomers. The process includes copolymerizing a first monomer having an aromatic moiety and an unsaturated alkyl moiety and a second monomer having an ionic moiety and at least one unsaturated moiety

In still another aspect, the present invention is an article of manufacture. The article is formed from a branched aromatic ionomer prepared by co-polymerizing a first monomer having an aromatic moiety and an unsaturated alkyl moiety and a second monomer having an ionic moiety and at least two unsaturated moieties. In this aspect, the ionic moiety has at least two ionizable groups, a cationic group that ionizes to form cations and an anionic group that ionizes to form anions and the cationic group is poly-valent and one capable of forming bridges to other molecules in the presence of ions of a suitable type and concentration.

Another aspect of the present invention is an article of manufacture. The article is formed from a branched aromatic ionomer prepared by co-polymerizing a first monomer having an aromatic moiety and an unsaturated alkyl moiety and a second monomer having an ionic moiety and at least one unsaturated moiety. In this aspect, the ionic moiety has at least two ionizable groups, a cationic group that ionizes to form cations and an anionic group that ionizes to form anions and the cationic group is a mono-valent group.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed understanding and better appreciation of the present invention, reference should be made to the following detailed description of the invention and the preferred embodiments, taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is graph of Conversion Versus Time during the runs made in Example 2;

FIG. 2 is a graph of the Molecular Weight Results during the runs made in Example 2:

FIG. 3 is a graph of the Melt Flow Results during the runs made in Example 2;

FIG. 4 is a graph of the Glass Transition Temperature Results during the runs made in Example 2;

FIG. 5 is a graph of the Conversion Verses Time for the runs made in Example 3;

FIG. 8 is a graph of the Molecular Weights Results for the runs made in Example 3;

FIG. 7 is a graph of the Glass Transition Temperature Results for the runs made in Example 3; and

FIG. 5 is a graph of the Melt Flow Results for the runs made in Example 3.

It will be appreciated that the figures are not necessarily to scale and the proportions of certain features may be exaggerated to show detail.

DETAILED DESCRIPTION OF INVENTION

The term “ionomer” is defined in the art of preparing polymers as a polymer with covalent bonds between elements of the polymer chain and ionic bonds between the separate chains of the polymer. Ionomer is also defined as polymers containing inter-chain ionic bonding. Thermoplastic ionomers have the unique property of forming reversible crosslinks. At melt processing temperatures, crosslinks disassociate to later reform as the material cools to its glass transition temperature.

Branched aromatic ionomers may be formed by co-polymerizing a first monomer having an aromatic moiety and an unsaturated alkyl moiety and a second monomer having an ionic moiety and at least one unsaturated moiety. For example, suitable monomers having an aromatic moiety and an unsaturated alkyl moiety may include monovinylaromatic compounds such as styrene as well as alkylated styrenes wherein the alkylated styrenes are alkylated in the nucleus or side-chain. Alphamethyl styrene, t-butylstyrene, p-methylstyrene, and vinyl toluene are suitable monomers that may be useful for preparing branched aromatic ionomers. The monovinylaromatic compounds may be employed singly or as mixtures. In one embodiment, styrene is used exclusively as the first monomer. Any monomer having an aromatic moiety and an unsaturated alkyl moiety may be used to prepare the branched aromatic ionomers.

The second monomer has an ionic moiety and at least one unsaturated moiety. The ionic moiety has at least two ionizable groups, one group that ionizes to form cations and one that ionizes to form anions. In one embodiment, the group that ionizes to form cations, hereinafter “cationic group,” is a mono-valent group. In another embodiment, the cationic group is poly-valent and one capable of forming bridges to other molecules in the presence of ions of a suitable type and concentration.

When the cationic group is a mono-valent group, if is a mono-valent metal or a quaternary ammonium ion forming compound. Suitable metals include sodium, potassium, cesium, silver, and the like. Suitable quaternary ammonium compounds include ammonium chloride, methyl ammonium chloride, diethyl ammonium chloride, and the like.

When the cationic group is one capable of forming bridges to other molecules in the presence of ions of a suitable type and concentration, it is a group that ionizes to form cations having a valence of +2 or higher. In one embodiment, the cationic group may be a metal having an oxidation state of +2 or higher. Suitable metals include zinc, copper, lead, calcium, magnesium, zirconium, aluminum, and the like.

The second ionizable group is an organic group that ionizes to form an anion having a coordination charge of −1 or lower. Suitable groups include the anions of amines, carboxylic acids, sulfonic acids, phosphonic acids, thioglycolic acids and the like. When the cationic group has a valence of greater than +1, the first and second ionizable groups may form a bridge.

The anionic group includes at least one polymerizable unsaturated moiety. In some embodiments, there is only one. In other embodiments, there may be two or more such moieties. The unsaturated moiety may be a terminal or non-terminal carbon-carbon double bond.

Exemplary compounds useful as the second monomer may be prepared with a metal cation and an organic anion having at least one unsaturation. Suitable compounds that may be used as the second monomer include any having a general formula:

wherein R is a hydrocarbon chain having from 2 to 40 carbons and at least one polymerizable unsaturation [Is this defined?]; A is an anionic group; M is a cationic group; Z is −1 or −2; X is +1, +2, +3, +4, or +5; and y is an integer having a value of from 1 to 4.

When y is 1, R may have one or more polymerizable unsaturations. In embodiments where y is 1, R may have two or more unsaturations and the unsaturations will either be on separate chains or else sufficiently far apart on a single chain to allow for polymerization without substantial steric hindrance. In some embodiments, (y*Z)+X=0, that is, only anionic groups having a polymerizable unsaturation will be coordinated to the M group, however if is within the scope of the claims that additional groups not having a polymerizable unsaturation may be coordinated to the M group. When this occurs, there may still be at least two polymerizable unsaturations coordinated to the M group in addition to any other coordinated groups.

Compounds that may be used as the second monomer of the present invention include, but are not limited to: zinc diacrylate, zinc dimethacrylate, zinc di-vinylacetate, zinc di-ethylfumarate, and the like; copper diacrylate, copper dimethacrylate, copper di-vinylacetate, copper di-ethylfumarate, and the like; aluminum triacrylate, aluminum trimethacrylate, aluminum tri-vinylacetate, aluminum tri-ethylfumarate, and the like; zirconium tetraacrylate, zirconium tetramethacrylate, zirconium tetra-vinylacetate, zirconium tetra-ethylfumarate, and the like. For compounds having monovalent cationic groups, the second monomer may be sodium acrylate, sodium methacrylate, silver methacrylate, and the like. These compounds and any compound useful as the second monomer may be prepared by, for example, reacting an organic acid or an anhydride with a metal or metal salt. When the cation group is polyvalent, then the organic acid and the polyvalent metal may be reacted under conditions sufficient to prepare a bridge between the anionic group and the cationic group. Compounds useful as the second monomer may be prepared by any method known to those of ordinary skill in the art of preparing monomers to be useful.

The monomers used to prepare the branched aromatic ionomers may interact in several ways to affect the physical properties of the ionomers. A first way is the formation of covalent bonds due to the polymerization of the unsaturated moieties.

A second way that the monomers used to prepare the branched aromatic ionomers may interact is by the formation of a bridge wherein a polyvalent cationic group is coordinated to two anionic groups which are integrated into the backbones of at least two separate chains. This coordination may, in effect, cross link the two chains thereby increasing that segment's total effective molecular weight to the sum of the two chains.

A third way that that the monomers used to prepare the branched aromatic ionomers may interact is by the formation of multiple bridges as described immediately above. The more crosslinking that occurs, the less flexible the three dimensional structure of the ionomer, which may result in lower melt flow values and increased melt strength.

In yet a fourth way of interacting, when the cationic groups are mono-valent, the ionic moieties, while not fully bridged, may still associate due to hydrophobic-hydrophilic forces. In these embodiments, this weaker but still measurable force may result from the comparatively non-polar hydrophobic, non-ionic parts of the molecule being mutually attracted and repelled from the polar hydrophilic ionic parts of the ionomer. These forces are more noticeable as the proportion of the second monomer is increased in concentration. These four are not all of the possible interactions of the monomers. In addition, most of the properties of the ionomers associated with its primary, secondary, and even tertiary structure, such as the ionomers' glass transition temperatures “Tg” may be affected.

Both the amount of second monomer and the type of interaction with the first monomer will dictate the amount of second monomer used. Therefore, in some embodiments where the interaction is weak, such as when the cationic group of the second monomer is mono-valent, and a significant amount of effect is desired from the second monomer, the branched ionomers are prepared with a comparatively large amount of the second monomer, typically with a ratio of first monomer to second monomer of from about 999:1 to about 40:60. In other such embodiments, the ratio is from about 95:5 to about 50:50. In still other such embodiments, the ratio is from about 90:10 to about 60:40. Other embodiments have a ratio of from 80:20 to 70:30. Where the interaction is very strong, such as when the cationic group is di- or tri-valent, or only small changes to the properties of the ionomer due to the second monomer are desired, the amount of the second monomer is quite small ranging from about 10 parts per million “ppm” to about 10,000 ppm. In other such ionomers, the range is from about 100 ppm to about 1000 ppm. In still other such ionomers, the range is from about 250 ppm to about 800 ppm.

The branched aromatic ionomer is prepared by co-polymerizing the first and second monomers. Each of these monomers has at least one polymerizable unsaturation. The polymerization may be carried out using any method known to those of ordinary skill in the art of performing such polymerizations. For example, the polymerization may be carried out by using a polymerization initiator.

Examples of the polymerization initiators are, for instance, radical polymerization initiators such as benzoyl peroxide, lauroyl peroxide, t-butyl peroxybenzoate and 1,1-di-t-butylperoxy-2,4-di-t-butylcyclohexane. The amount of the polymerization initiator is from about 0 to about 1 percent by weight of the monomers. In one embodiment, the amount of polymerization initiator is from about 0.01 to about 0.5 percent by weight of the monomers. In another embodiment, the amount of polymerization initiator is from about 0.025 to about 0.05 percent by weight of the monomers.

Alternatively, rather than using an initiator, the ionomer may be prepared using heat as an initiator. The ionomer may be prepared using a non-conventional initiator such as a metallocene catalyst as is disclosed in U.S. Pat. No. 6,706,827 to Lyu, et al., which is incorporated herein in its entirety by reference. In one embodiment, the monomers may be admixed with a solvent and then polymerized. In another embodiment, one of the monomers is dissolved in the other and then polymerized. In still another embodiment, the monomers may be fed concurrently and separately to a reactor, either neat or dissolved in a solvent, such as mineral oil. In yet another embodiment, the second monomer may be prepared in-situ or immediately prior to the polymerization by admixing the raw material components, such as an unsaturated acid or anhydride and a metal alkoxide, in-line or in the reactor. Any process for polymerizing monomers having polymerizable unsaturation know to be useful to those of ordinary skill in the art in preparing such polymers may be used. For example, the process disclosed in U.S. Pat. No. 5,540,813 to Sosa, et al., may be used and is incorporated herein in its entirety by reference. The processes disclosed in U.S. Pat. No. 3,660,535 to Finch, et al., and U.S. Pat. No. 3,658,946 to Bronstert, et al., may be used and are both incorporated herein in their entirety. Any process for preparing general purpose polystyrene may be used to prepare the branched aromatic ionomer ionomers.

In certain embodiments, the ionomers may be admixed with additives prior to being used in end use applications. For example, the ionomers may be admixed with fire retardants, antioxidants, lubricants, blowing agents, UV stabilizers, antistatic agents, and the like. Any additive known to be useful to those of ordinary skill in the art of preparing ionomers to be useful may be used with the branched ionomers.

The ionomers are useful as general purpose polystyrene, but may also be used in other applications. They may be foamed to prepare foamed polystyrene. The ionomers may be used in applications where high temperature performance is desirable such as microwave safe dishes and utensils. The ionomers may be used to form other objects such as containers and as components in automobiles, toys, and the like. The polar ionic moieties of the ionomers may enhance their compatibility with polyesters such as polyethylene terephthalate and polycarbonate, so the branched ionomers may be used in blends and alloys with these and other similarly polar polymers.

EXAMPLES

The following examples are provided to illustrate the present invention. The examples are not intended to limit the scope of the present invention and they should not be so interpreted. Amounts are in weight parts or weight percentages unless otherwise indicated.

Example 1

Polystyrene homopolymer is prepared using a stirred 500 ml reaction kettle. The polymerization is initiated using a LUPERSOL® 233 catalyst at a concentration of about 170 ppm. The reaction is run at about 267° F. (131° C.). The initial melt flow of the polystyrene is 3.7 dg/minute. Zinc dimethacrylate “ZnMA” is added in stages by first dissolving the ZnMA in styrene and then feeding the solution to the reactor. The reactor is allowed to stabilize and samples are collected at points where the concentration of ZnMA in styrene is 400 ppm, 600 ppm and 800 ppm. The samples are tested and the results shown below in Table 1.

Example 2

Example 1 is repeated substantially identically except that the reaction is run at 275° F. (135° C.), and 175 ppm of LUPERSOL® 233 catalyst, and the components shown in Table 2 are used. The n-dodecyl mercaptan (NDM), serves as a chain transfer agent. The samples are tested and the results shown below in Table 2.

Example 3

Polystyrene is prepared using a constant concentration of methacrylic acid using the same procedure and apparatus as in Example 2 except that the acid is neutralized in the feed with bases that have different valences: sodium ethoxide, calcium carbonate, aluminum(III) isopropoxide, and zirconium(IV) isobutoxide, and the LUPERSOL® 233 catalyst is used at a concentration of 200 ppm. The samples are tested and the results shown below in Table 3.

TABLE 1 Example 1-A Example 1-B Example 1-C [ZnMA] ppm 400 600 800 MRI¹ NA 3.84 3.51 Flex Strength² NA 13,808/95.2  13,377/92.2  Tensile Strength Yld³ NA 7,421/51.2 7,409/51.1 Tensile Strength Brk³ NA  7326/50.5 7,290/50.5 Elongation³ NA 3.0 2.5 Vicat⁴ NA 220/104 220/104 Mn⁵ 94 95 94 Mw⁵ 249 298 315 Mz⁵ 424 1978 2,433 Polydispersity⁶ 2.6 3.2 3.3 ¹ASTM D-1238 g/10 min, 200 C/5 kg, October 2001. ²ASTM D-790 psi/MPa, January 2001 ³ASTM D-638 psi/MPa, psi, %, September 2001 ⁴ASTM D-1525, F/C, May 2000 ⁵ASTM D-6474 ⁶Mz/Mn

TABLE 2 Comp-2* 2-A 2-B 2-C 2-D 2-E [ZnMA] ppm 0 1200 1200 1800 4000 5000 NDM ppm 0 0 100 150 440 550 MFI¹ 4.4 3.2 4.0 2.8 0.8 0.7 Tg² 107 114 113 113 109 113 Mn³ 107 108 93 96 97 93 Mw³ 222 269 307 354 413 405 Mz³ 335 1867 3754 4963 4763 4849 Polydispersity⁴ 2.1 2.5 3.3 3.7 4.2 4.3 ¹ASTM D-1238 g/10 min, 200 C./5 kg, October 2001. ²ASTM D-3418, C, DSC Inflection (Mid) Point, July 1999. ³ASTM D-6474 ⁴Mz/Mn. *Not an example of the invention.

TABLE 3 3-A 3-B 3-C 3-D Comp-3* Na Salt Ca Salt Al Salt Zr Salt Methacrylic Acid, NA 1269 1269 1269 1269 ppm Sodium, ppm¹ NA 339 NA NA NA Calcium, ppm² NA NA 295 NA NA Aluminum, ppm³ NA NA NA 132 NA Zirconium, ppm⁴ NA NA NA NA 336 Melt Flow⁵ 2.90 2.39 2.70 1.80 0.51 Tg⁶ 107.5 108.0 108.6 109.3 109.7 Mn⁷ 124,563 119,328 126,800 129,454 114,417 Mw⁷ 256,581 262,625 235,875 608,260 1,044,123 Mz⁷ 391,336 400,917 613,472 6,737,117 10,494,556 PDI⁸ 2.1 2.2 2.3 4.7 9.1 ¹as sodium ethoxide ²as calcium carbonate ³aluminum(III)isopropoxide ⁴zirconium(IV)butoxide ⁵ASTM D-1238 g/10 min, 200 C./5 kg, October 2001. ⁶ASTM D-3418, C, DSC Inflection (Mid) Point, July 1999. ⁷ASTM D-6474 ⁸Mz/Mn. *Not an example of the invention.

Discussion of the Figures

FIGS. 1-4 are graphical representations of the values recorded relating to Example 2. Therein, zinc di-methacrylate is shown to be an effective di-functional monomer to induce chain-branching and to increase the z-average molecular weight in polystyrene. Levels as low as 200 ppm increased the z-average molecular weight of the polystyrene to close to 1,000,000 g/mol. Despite the efficiency of this monomer as a crosslinking agent, the resulting polymers did not show signs of gelation at levels of addition producing molecular weights of up to 8,000,000 g/mol.

FIGS. 4-8 are graphical representations of the values recorded relating to Example 3. They show that various salts of methacrylic acid may be synthesized, in-situ, in the polymer feed, prior to polymerization. They also show that in going from a mono-valent to a tri-, or tetra-valent counter-ion, the weight average molecular weight is observed to double or triple, and the and z-average molecular weight is observed to increase up to 20 fold. It is observed that in going to higher valence states, the increase in molecular weight is accompanied by a decrease in the melt flow, however, even for molecular weights of 1,000,000 g/mol, the material still flows. 

1-22. (canceled)
 23. A branched aromatic ionomer comprising the product of co-polymerizing a first monomer comprising an aromatic moiety and an unsaturated alkyl moiety and a second monomer represented by the general formula:

wherein M is a main group or transition metal with a valence of x, O is oxygen, R₁, R₂, R₃ and R₄ are selected from hydrogen, alkyl groups, aryl groups or combinations thereof, x is selected from +1, +2, +3, +4 or +5 and n is an integer having a value of from 1 to
 4. 24. The branched aromatic ionomer of claim 23, wherein the first monomer is selected from styrene, alphamethyl styrene, t-butylstyrene, p-methyl styrene, vinyl toluene, and mixtures thereof.
 25. The branched aromatic ionomer of claim 23, wherein the first monomer is styrene.
 26. The branched aromatic ionomer of claim 23, wherein the second monomer is selected from zinc diacrylate, zinc dimethacrylate, zinc di-vinylacetate, zinc di-ethylfumarate, copper diacrylate, copper dimethacrylate, copper di-vinylacetate, copper di-ethylfumarate, aluminum triacrylate, aluminum trimethacrylate, aluminum tri-vinylacetate, aluminum tri-ethylfumarate, zirconium tetraacrylate, zirconium tetramethacrylate, zirconium tetra-vinylacetate, zirconium tetra-ethylfumarate and mixtures thereof.
 27. The branched aromatic ionomer of claim 23, wherein the second monomer is zinc diacrylate.
 28. The branched aromatic ionomer of claim 23, wherein the second monomer is zinc dimethacrylate.
 29. The branched aromatic ionomer of claim 23, wherein the second monomer comprises zirconium tetraacrylate.
 30. The branched aromatic ionomer of claim 23, wherein the second monomer comprises zirconium.
 31. The branched aromatic ionomer of claim 23, wherein the second monomer comprises at least two unsaturated moieties.
 32. An end use article formed by the branched aromatic ionomer of claim 23 selected from sheets, foamed articles, oriented films and combinations thereof.
 33. A process for preparing a branched aromatic ionomers comprising copolymerizing a first monomer comprising an aromatic moiety and an unsaturated alkyl moiety and a second monomer represented by the general formula:

wherein M is a main group or transition metal with a valence of x, O is oxygen, R₁, R₂, R₃ and R₄ are selected from hydrogen, alkyl groups, aryl groups or combinations thereof, x is selected from +1, +2, +3, +4 or +5 and n is an integer having a value of from 1 to
 4. 